My thinky thoughts inspired by the first two Mirage of Blaze stage plays continue, and in this post I want to talk principally about the construction of Kagetora's emotional-sexual needs as informed by the context of the plays.
Mirage SPOILERS follow:
I don't think we can discuss Kagetora's sexual identity without discussing his emotional needs and vice versa. He's extremely demisexual: his sexual attraction to someone is hugely dependent on his interpersonal emotional need for them. Thus, he is attracted to Naoe in his Yoshiaki body but not really to Kotarou!Naoe in what he perceives as the same body. To be sure, he makes passes at Kotarou, but these are an attempt to resurrect Naoe's prior behavior patterns, not a sign of intrinsic attraction. In fact, Kotarou!Naoe puts him off. Conversely, he is attracted to Naoe in Kaizaki's body because of his Naoe-like behavior. The body itself is not very germane. I gather that he is attracted to Minako too, who is in a very different type of body but is also someone who meets a certain interpersonal need.
Now, Kagetora also loves people he is not sexually attracted to: the other three Yashashuu, Yuzuru, Miya, Kenshin, Ujiteru, for example. But he loves them all from the vantage point of being a protector or leader or otherwise trying to prove himself. They are all people with whom he feels he cannot share his weakness or his problems, at least not fully. The people to whom Kagetora can become sexually/romantically attached—the only examples I know of are Naoe and Minako—are people to whom, ultimately, he can reveal his weakness, people he is willing to turn to for support. (It's worth noting that as long and arduous as his history with Naoe is, he only really begins to accept that he wants a sexual relationship with him about the time he begins to embrace Naoe as someone who is truly there for him and not going to leave.)
For Kagetora, his ability to embrace sexual attraction is fairly synonymous with being willing to show that he is weak, i.e. sexuality is aligned with weakness. This makes perfect sense given his personality and background.
Kagetora was gang raped as a teen in his original life, and—owing to an unfortunate confluence of circumstances and personality—this fundamentally shaped his sexual identity for 400 years. He has several painful flashbacks to it in his life as Takaya, for example. Kagetora's view of his own sexuality is heavily negative, at least up through almost all of what's translated into English (~vol. 24). This is perhaps most clearly illustrated in vol. 21, in which Takaya is pretty much going through sexual withdrawal from being without Naoe and has some extremely dark thoughts about the nature of his own sexual desire: "Worse… than a beast," etc. And this is Takaya after he has come to terms with wanting Naoe and had tons of sex with Naoe, and at least somewhat gotten past his core fear of being penetrated.
The way I read this, Kagetora's fundamental model for sex is rape, which is to say, he views penetration as inherently violent and being penetrated as inherently violating. (By the way, I don't mean he sees sex this way intellectually in his judgments about in other people's lives; I mean this is his basic emotional response in his own life.) For most of his life, this makes sex rather a pickle because he can't win no matter what he does. If he's in a traditional sexual relationship with a woman, I can only image he feels rather guilty about penetrating her. I don't have textual evidence for this except that he seems to avoid sexual relationships with women. He was historically twice married and had, at least, five children, so it's plain he could function sexually, but when not forced into arranged marriages, he seems largely celibate.* And, if he is in danger of being penetrated, he feels raped: tons of textual evidence for this. This is, of course, a great psychological barrier he breaks through with Naoe: becoming able to be a consenting uke. But this comes late in his career and is a hard-won transformation.
So this is the basic arc for Takaya—up through approximately what's been translated into English: without his memories, he basically has Kagetora's mindset without his specific experiences. As his memory comes back bit by bit, he must journey from being (understandably) horrified by Naoe's sexual assaults to recognizing that he wants Naoe to finally being able to be in a consensual, mutually responsible sexual relationship with him. There's a middle zone in here that reads as "please ravish me," a stage in which Takaya is aware of a strong desire for Naoe but is not quite able to take responsibility for consenting to have sex with him. And this stage makes sense for someone whose model for allowing himself to be penetrated is consenting to his own rape. It makes sense too for someone whose view of his sexuality is dark in general and who, thus, views succumbing to sexual desire as a weakness.
The context of the plays:
The plays take place about thirty years before we first see Takaya and his dynamic with Naoe. They present the foundation for that dynamic. Some of the patterns are the same: Kase!Kagetora asserts his dominance verbally over Kasahara!Naoe, who not infrequently responds by tackling him, in one instance tackling him to the floor in an overtly sexual manner. Kase shares with Takaya the curious habit of never actually fighting back against these tackles. Both of them grapple at first and then give up. And while it's fair to say that both Kagetoras are physically weaker than both Naoes, we are nonetheless assured again and again that no one in the Yashashuu has greater spiritual powers than Kagetora—and he uses them to fend off others. So, yes, he could fight back.
With Takaya, it's easiest to read the tokenism of his resistance as a sign that much of him doesn't want to resist. He's increasingly ready to be ravished by Naoe. With Kase, I'm inclined to think the answer is the same: part of him wants this from Naoe. But that part is more repressed, more held in check by his rational control.
And this, I think, gets to the essence of Kase. He is Kagetora, with the same foundational trauma. He has just not reached the terminal stage of meltdown that defines much of Takaya's experience. Like Takaya, Kase has adopted a survival strategy that doesn't work: one predicated on always being in control of himself, always being competent at the work, and never letting his own needs or weakness show, at least not beyond moments of sadness. For Takaya is it painfully obvious that this strategy isn't working: he has to bury his memories and put spells on himself to function; his soul is coming apart in little "tangerine" fragments; he's weeping to putative strangers about this guy he's hung up on; he's losing control of his powers, and so on.
For Kase, it also isn't working, but he hasn't yet used up all his reserves. He's burning them faster than he's replenishing them, but they're not gone yet. Therefore, he can put on a much better pretense of actually being in complete control of himself, of always being on-point in doing the Yashashuu stuff, of always being the strong one. Naoe gets that this is an act, but I don't think he gets how much. I don't think he really has access to how profoundly wounded Kagetora is. And, thus, he doesn't have the same entry point into Kase's life as he will into Takaya's. Kase is better at pretending not to need him, at least not that much, and the strength of that pretense keeps Naoe more or less at bay—which is one of things it's designed to do: as long as Naoe does not get too close, Kagetora can continue to pretend he's always stronger.
This strategy does, in fact, make Kagetora very effective as a leader—until it stops working. But it comes at the psychological cost of never having his emotional needs met, of always being emotionally alone. Takaya (due in part to lacking Kagetora's memories) is kind of done with this. From very early on, he is open to leaning on Naoe with a very un-Kagetora-like vulnerability. This diminishes when he gets his memories back, but the basic pattern is set. Kase cannot do this and, thus, though he's overtly more stable than Takaya, he may, in fact, be emotionally needier. He gets no relief. He is always performing a role unless he is completely alone. He is hungering, I think, for someone he can be open with.
From this context, it makes perfect sense that he would attach so powerfully to Minako. The general explanation I've heard of their relationship is that he bonded with her because she was psychologically safe and nonjudgmental, and that sounds completely right. From what I've seen/read of her, Minako is genuinely very sweet in a traditionally supportive female way but with the will to deal with the crazy that surrounds the Yashashuu. At least, she doesn't run screaming. Kagetora cannot be weak with Naoe in this period because that would disempower him, but he can, I think, be weak with Minako, and she doesn't judge him or abandon him, which is exactly the kind of validation he needs and the kind of respite he needs from being indefatigably strong. Thus, I image, she becomes profoundly important to him because she is his one true source of relief.
* I seem to recall reading in some summary/discussion of the Minako era that Naoe had been aware of Kagetora having lovers in the past but none had seemed serious like Minako. I'm not sure how to read this. It feels out of character based on what I've personally encountered, but I'm surely willing to be educated by further context. As for Minako, I don't have a clear sense of their sexual dynamic. I seem to have read assertions both that they did and did not actually have sex. Again, I'm very willing to be educated.